I can’t speak for the 17-40 but I found the 16-35 2.8 II to be an average lens at best. It was my first UWA, so while the range was cool, I never truly enjoyed the images I got out of that lens. I found the corner/off-center sharpness to be lacking.

When the f4 IS came out, I traded in the old 2.8 for it. The IS and the vastly superior IQ more than made up for the loss of stop. I’d still have it now if it weren’t for a sweet deal on version III of the 2.8 (refurb) that I took advantage of a couple months ago...

Unless you NEED f2.8, the f4 IS is the better lens (compared to 2.8 II) in every which way. IMO of course.

I can’t speak for the 17-40 but I found the 16-35 2.8 II to be an average lens at best. It was my first UWA, so while the range was cool, I never truly enjoyed the images I got out of that lens. I found the corner/off-center sharpness to be lacking.

When the f4 IS came out, I traded in the old 2.8 for it. The IS and the vastly superior IQ more than made up for the loss of stop. I’d still have it now if it weren’t for a sweet deal on version III of the 2.8 (refurb) that I took advantage of a couple months ago...

Unless you NEED f2.8, the f4 IS is the better lens (compared to 2.8 II) in every which way. IMO of course.

Out of interest Act444, how do you find the MkIII compares against the f/4 (excluding the ability to open to f/2.8 ) ? Is there much else to choose between them?

Out of interest Act444, how do you find the MkIII compares against the f/4 (excluding the ability to open to f/2.8 ) ? Is there much else to choose between them?

The f/2.8L III is that extra bit sharper -- it's quite a lens.

However, note that vignetting is staggering at 16mm f/2.8, in excess of 4 stops. It's correctable in post, of course, but boosting the corners of an already high ISO file by 4 additional stops (say, for astro) is not super desirable.

Out of interest Act444, how do you find the MkIII compares against the f/4 (excluding the ability to open to f/2.8 ) ? Is there much else to choose between them?

The f/2.8L III is that extra bit sharper -- it's quite a lens.

However, note that vignetting is staggering at 16mm f/2.8, in excess of 4 stops. It's correctable in post, of course, but boosting the corners of an already high ISO file by 4 additional stops (say, for astro) is not super desirable.

I have pretty much decided on the Tamron 15-30 f2.8 SP and am waiting for a trade-in from KEH (who are being very slow). However today Sigma announced the new 12-24 f2.8 Art, which gives me another option to consider. I wonder how long it will be before they announce pricing and availability and how long before testers start posting reviews?

I have the Tamron and it is an excellent lens. Just don't forget that if you use filters it will cost you. All that said: When I went to the camera shop in Las Vegas I went with the intention of getting the Canon 11-24. I'd read reviews of both lenses and from those I felt safe getting the Tamron at that big price difference.

If I had it to do over again which would I pick? The Canon. Why? From what I understand there is no keystoning at all. That's huge to me. I somehow missed that very important tidbit.

I can't speak to the other lenses, but there are a lot of people here that really like the 16-35 f/4.

Isn't Tilt/Shift the only way to avoid keystoning? I don't think any standard wide angle lens can avoid keystoning.